Scatterings

A Nano Alternative to LEDs for Solid-State Lighting

Yvonne Carts-Powell

David Carroll and Greg Smith (black shirt) work on lighting technology based on field-induced polymer electroluminescence.

Adding a few carbon nanotubes to a polymer film can make a big difference in its electronic abilities, which allows the film to produce more light when part of a field-induced polymer electroluminescence (FIPEL) device. A paper from Wake Forest University (U.S.A.) and Trinity College Dublin (Ireland) researchers is scheduled for publication in January (Org. Electron., doi: 10.1016/j.orgel.2012.10.017).

Organic materials are attractive for lighting because they can be produced and processed inexpensively, and organic LEDs have been pursued because of this, but their lifetimes continue to be problematic. Thin film electroluminescent materials might have longer lifetimes—researcher David Carroll reports having one that has lasted a decade. Because FIPELs are, essentially, a capacitor with a light emitting layer and one or two dielectric layers between the electrodes, the dielectric layers may be able to reduce the reactions between the active layer and electrodes, as well as protecting the active layer from atmospheric degradation from oxygen or moisture.

The device runs on AC current. To lower the energy barriers to electron injection, they added a few carbon nanotubes. The performance was much better when a few nanotubes were added: luminance was five times brighter, increased from 20 cd/m2 to about 100 cd/m2 when a few (0.04 wt%) nanotubes were added to the emissive layer. The devices operated most efficiently at 80 Hz, although operation at 60 Hz (i.e., U.S. house current) was also high.

The researchers say the new lighting solution is at least twice as efficient as compact fluorescent bulbs and on par with LEDs.Wake Forest is working with a company to manufacture the technology and plans to have it ready for consumers in the next year.